This is a story based achievement that cannot be missed. You will seek the first relic in the Jade Temple and will have to fight Muneco near the end of this temple. After the temple guardian squishes about a dozen baddies with his foot, you'll enter a door to face the boss. The fight is relatively straight forward in which he will launch chickens personally or have them sweep across the screen but can be punched whenever he is "normal" sized. It should pop right after he crumples to the ground.